Re: [PATCH] tps65910: Work around silicon erratum SWCZ010

[Arnout Vandecappelle <arnout@mind.be>]

On 08/22/14 15:46, Laxman Dewangan wrote:
> On Friday 22 August 2014 05:44 PM, Arnout Vandecappelle (Essensium/Mind) wrote:
> >  From http://www.ti.com/lit/pdf/SWCZ010 :
> >
> > Glitch on SDA-SCL not managed correctly by the I2C IP
> >
> > Impact:
> > The standard specifies that the I2C transfer should restart on a start
> > event in all cases. The current design does not support two consecutive
> > Start conditions. This can cause the first real access after such a
> > glitch to be corrupted.
> >
> > Description:
> > An unexpected glitch on SDA and SCL can generate a wrong start event.
> > In the current design, the SCL line must toggle two times to detect a
> > new start event and completely restart the I2C access; hence the real
> > start event is not detected in the case of a single SCL toggle.
> >
> > Workaround:
> > Repeat I2C access.
> >
> > The first access to the tps65910 that we do is when loading the regmap
> > in the probe function. If there has been a glitch during boot and the
> > erratum is triggered, then the regmap loading will fail with -REMOTEIO
> > since the I2C transfer is not ACKed by the tps65910.
> >
> > A simple retry will work around it, because a subsequent I2C start
> > condition is detected properly by the tps65910.
> >
> > Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
> > ---
> > This patch is based on v3.17-rc1.
> > Build-tested with omap2plus_defconfig.
> > Runtime tested based on v3.4.97 with a custom config.
> > ---
> >   drivers/mfd/tps65910.c | 12 +++++++++++-
> >   1 file changed, 11 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/mfd/tps65910.c b/drivers/mfd/tps65910.c
> > index f243e75..cc1ca33 100644
> > --- a/drivers/mfd/tps65910.c
> > +++ b/drivers/mfd/tps65910.c
> > @@ -487,8 +487,18 @@ static int tps65910_i2c_probe(struct i2c_client *i2c,
> >       tps65910->id = chip_id;
> >   
>
> I think one dummy read of any register unconditionally before regmap init will
> resolve this issue.
> Similar issue we face with Palmas TPS65913 and TI recommended to use dummy read
> before any valid transfer.
>

 Yeah, good idea.

 So something like

i2c_master_send(i2c, "", 1);

just before the regmap_init.

 Is abusing the empty string like that OK or should I declare a dummy buffer?

 Regards,
 Arnout


-- 
Arnout Vandecappelle arnout at mind be
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